8. The dust-free case: surface stress

The maximum value of instantaneous surface 
stress reaches 0.04 Pa (Fig.4).

It is equal to the threshold value to raise dust
from the surface obtained by wind tunnel 
experiment (Greeley & Iversen, 1985).

Surface stress which exceeds the threshold 
value may be achieved more easily in the 
presence of background wind (Fig 5).  



Fig.5: Horizontal distributions of the absolute value of surface stress 
obtained at LT = 16:19. Blue line is the calculated stress. Purple and 
green lines represent the values where 10 m/sec background parallel 
and normal winds are superposed with the calculated wind. Red and 
orange lines are the same as Fig.4.



Fig.4: The diurnal change of absolute value of surface    
stress under dust-free condition. Blue line is the            
maximum value in the horizontal direction, light blue      
line is the horizontal mean value. Red and orange lines  
are upper and lower limit of critical surface stress           
(Greeley & Iversen, 1985).